1. Technical Field
The present invention relates to apparatus, methods, and devices for use in characterizing a free-space electromagnetic field, and in particular, to apparatus and methods suitable for real-time two-dimensional far-infrared imaging applications.
2. Related Art
In the ever more dangerous environment that exists in international relations that prevails in the early 21st century, the detection of explosive devices and the explosive compounds they contain has become critical. The development of efficient explosive sensing devices with state-of-the-art science and technology is a top priority among many defense related research and development projects. Among the many techniques being pursued, the use and sensing of terahertz (THz) radiation has proven to be innovative sensing and imaging technology. The use and sensing of THz radiation can provide spectroscopic information of most explosives and their related compounds, promising for the standoff detection and identification of explosive, and non-explosive, targets.
THz technology is well accepted by both industry and government for use for non-destructive evaluation (NDE), imaging, and sensing of materials which exhibit spectral fingerprints in the THz frequency range. Most materials which exhibit such fingerprints are drugs, explosives and related compounds, and other hazardous materials. For example, more than 14 explosives and their explosive related compounds (ERCs) have been measured by using THz wave time-domain spectroscopy, their spectroscopic signatures in THz frequency range have been reported in the literature.
However, typical prior art THz systems have very limited portability and mobility due to the large size of, for example, their Ti:sapphire lasers commonly used, and due to the size of their required laser power supply and cooling systems. In addition, most pulsed THz systems are designed using free-space delicate optics, making them extremely sensitive to any vibrations, pressures, and torque loadings. Typical prior art THz systems are bulky, heavy, and are not user friendly, even though they may use compact and turnkey pulsed fiber lasers. The demand for THz technology comes from research, industrial, and military applications where the operator is not expected to have experience in advanced optical systems. By its nature, traditional THz time-domain systems are quite complex and difficult to keep optimized. For most field applications, especially for defense applications, a mobile, robust, turnkey, miniature, or handheld THz time-domain spectrometer is essential. Aspects of the present invention provide such a system.